1. Field of the Invention
The present invention relates to tracking movement of a magnetic tape, and more specifically to demodulating servo track information on the tape.
2. Related Art
Mass storage devices and media require increased data storage capacity and retrieval performance. As to linear tape recording, in particular, a popular trend is toward multi-head, multi-channel fixed head structures with narrowed recording gaps and track widths, so that many linear tracks may be achieved on a tape medium of predetermined width.
Because of relatively high linear tape velocity, and because tape substrates continue to be made progressively thinner, guiding tape past a tape head structure along an accurate invariant linear path has become progressively more challenging. One tracking error phenomenon is known as lateral tape motion (“LTM”). An optical servo controller may be employed to track lateral motion of the tape relative to a recording head, as described in U.S. Pat. No. 6,246,535, to Saliba, et al., entitled “Optical Apparatus for Tracking a Magnetic Tape,” incorporated by reference herein in its entirety. To this end, the tape may include an optically detectable servo track that can be placed on the non-magnetic side of the tape, for example. An optical pickup head detects laser light reflected from the marks of the servo track. In response, the optical servo controller controls lateral head position to align the recording head with the magnetic track on the tape. By tracking lateral tape motion, this technique allows for narrower track width and thus greater storage density on the tape.
One problem with servo track detection is noise on the signal representing the light reflected from the servo marks. A peak detector is typically employed to detect the peak reflectivity from each mark, to thereby establish the position of the mark. However, noise on the peak can result in misdetection of the peak position. Improvement in the signal to noise ratio of the detected peak could lead to finer detection resolution in the lateral direction, allowing for narrower data track widths and greater storage density on the tape.